Process of decolorizing tar base distillates with aldehyde



May 8, 1956 w. E. KEMP 2,744,857

PROCESS OF DECOLORIZING TAR BASE v DISTILLATES WITH ALDEHYDES Filed March 19, 1954 2 Sheets-Sheet 1 e f a,

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PROCESS OF DECOLORIZING TAR BASE DISTILLATES WITH ALDEHYDES Filed March 19, 1954 2 Sheets-Shae! 2 SOLVENT A1 BENZENE:

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. i Patented May 8, 1956 PROCESS OF DECOLORIZING TAR BASE I DISTILLATES WITH ALDEHYDE Woodrow E. Kemp, Pittsburgh, Pa., assignor to Koppers T Company, Inc., a corporation of Delaware Application March 19, 1954, Serial No. 417,400 12 Claims. (Cl. 20257) commercial standpoint.

Conventional decoloration techniques such as, for example, treatment with activated charcoal, oxidation with potassium permanganate, etc. have proven to be unsuccessful. Oxidation with potassium permangante was attempted on a plant scale but the permanganate salted out on the steam coils of the still, and it was impossible to carry out the distillation.

It is'therefore an object of the present invention to provide a process for decolorizing low-boiling coal-tar base distillates such as, for example, pyridine, picolines,

lutidines, etc., to produce distillate fractions of these materials which are practically colorless.

Another object of this invention is to provide a purifying technique which can be employed simultaneously with fractional distillation of the mixed low-boiling tar bases.

A further object is to provide a process which will obviate the difficulties of the prior art.

Ancillary and additional objects and advantages will be apparent as the invention is hereinafter-described in more detail.

It has now been discovered that the color-forming impurities in mixtures of mononuclear low-boiling tar bases having a pyridine nucleus and boiling at a temperature of at least about 115 C. can be removed by treating these mixtures with an aldehyde such as formaldehyde, acetaldehyde, propionaldehyde, heptanoic aldehyde, benzaldehyde, toluic aldehyde, etc., preferably an aldehyde containing no more than twelve carbon atoms, and thereafter separating, by fractional distillation, the tar bases from the higher boiling reaction products of the impurities. In addition to the foregoing aldehydes, polymeric aldehydes such as paraformaldehyde and para- United States Patent Oflice the amount of impurities present in the tar bases advantageously being determined by means of the p-dimethyl- .aminobenzaldehyde test. The p-dimethylaminobenzaldehyde test involves theme of Eh richs reaction and is carried out in the following manner. Three cc. of the .tar base sample is dissolved in 10 cc. of benzoil. Two ,cc. of alcoholic solution containing 1% p-dimethylaminobenzaldehyde is then added to the solution. Thereafter 0.5 cc. of hydrochloric acid is added to this solution, and the resulting solution is agitated for several minutes.

'The aqueous layer becomes violet-red in the presence of pyrroles 'or,,indole. By preparing suitable standards containing known amounts of pyrroles and comparing colors developed with the standards in a colorimeter, thev test is made quantitative. This .test is described in The Merck Index, 5th Edition, page 705.

The term approximately stoichiometric amount is used rather'broadly herein to include (1) the exact stoichiometric amount, (2.) where convenient or desirable, an amount containing an excess over the exact stoichiometric amount, and (3), when product specifications areless rigid so as to permit. certain small amount of discoloratiomthen less than the exact stoichiometric amount can be used. The distillation can be effected in either a batchwise or a continuous. manner. If the distillation is batchwise, the aldehyde can be added directly to the .mixture of low-boiling tar bases in the still. If the tar bases contain water, benzene, etc., is added to the still to prevent the formation of an azeotropic mixture of water and pyridine and distillation is carried out, taking offfirst an azeotropic mixture of benzene and water, then taking off fractions of (1) pyridine, (2) alphapicoline, (3) beta and, gamma picoline and 2,6-lutidine, and (4) taking off the remaining lutidines and collidines at progressively higher temperatures. In the practice of the'invention the various tar bases can also all be taken off as one fraction or as separate fractions regardless of whether the distillation is batchwise or a continuous one.

In a continuous operation, it is advantageous to treat the incoming low-boiling tar bases with the aldehyde in a reaction chamber operated either continuously or batchwiseand thereafter subject the mixture of tar bases and reaction products to continuous distillation.

If the low-boiling tar bases contain water as an impurity, the mixture of tar bases and reaction products is-passed to a first still where benzene is added to the mixture to form an azeotropic mixture with the water i present therein, and this azeotropic mixture taken off as aldehyde can be utilized to give the same reaction as the I dines, and collidines and mixtures of these compounds.

The amount of formaldehyde or other aldehyde that is utilized will obviously vary with the amount of colorforming impurities in the mixture of low-boiling tar bases,

- liquid, residue.

tion product if no water was present, is passed to a' overhead. The low-boiling tar bases are taken off as This liquid residue, or the original reacsecond still where pyridine is taken ofi as an overhead fraction, and the remaining tar bases taken oif as liquid residue and passedto a third still. In this third still alpha-picolineis taken oif as overhead, and the liquid residue passed to a fourth still where the beta and gamma picolines, lutidines, and collidines are taken off as overhead leaving the high-boiling impurities in the still residue.

The aldehyde can be, added directly to the still or to the reactor as such or can be added to the still or reactor dissolved in a suitable solvent such as, for example, water, methanol, ethanol, etc. However, when acetaldehyde, paraldehyde or mixtures thereof are utilized, it has been found to be advantageous not to utilize water. Formaldehyde can also be added directly to the low-boiling tar bases as a gas.

The invention can be more thoroughly understood by reference to the accompanying drawings. In the continuous process exemplified by the flow sheet of Fig. 1,

the low-boiling tar base mixture is continuously fed into a reactor 1 through a valved feed inlet 2 and a solution of formaldehyde in water is added to the reactor through a valved inlet line 3 from a dissolver 4. At the start of the process the water or other solvent is fed into the dissolver through a valved inlet line 5. The reactor can be provided with suitable agitating means such as, for

example, a three-blade marine-type propeller to insure complete contact andreaction of the formaldehyde with the impurities. The mixture of tar bases and reaction product. is continuously: withdrawn from the reactor through a valved line 6 and fed to a dehydrator column 7. Benzene is continuously fed to the column 7 through a line 8 from a storage tank 9 in an amount at least sufficient to form an azeotropic mixture with the water utilized as a solvent and the water which is already present in the impure low-boiling tar bases. The azeotropic mixture of benzene and water is continuously taken oif the top of column 7 through a line 10, heat being provided to accomplish this by a heater 11. The low-boiling tar bases and formaldehyde reaction products accumulate in the bottom of the column 7 and are continuously withdrawn from the column through a valved exit line 12 and fed to the column 13 where pyridine distills from the mixture. The pyridine vapors pass from the column 13 through line 14 to a condenser 15 from which colorless pyridine is removed by means of a valved exit line 16. A portion of the condensate is returned to the column 13 as reflux material through a valved line 17 and the remaining condensate is withdrawn through line 16 as colorless product pyridine. If the pyridine product should still contain some color, the amount of formaldehyde added to the reactor is increased to the point where the color disappears. The liquid residue in the bottom of the column 13 is continuously withdrawn from this column through a valved exit line 18 and passed to a column 19 where alpha-picoline distills from the mixture. The vapors pass from the column 19 through a line 20 to a condenser 21 from which colorless alpha-picoline is removed by a valved exit line 22. A portion of this alpha-picoline is returned to the column 19 as reflux material through a valved line 23 and the remaining condensate is removed through line 22 as colorless product alpha-picoline. If color still remains in the product alpha-picoline, however, the amount of formaldehyde added to the reaction chamber is increased to a point where the product alpha-picoline condensate becomes colorless. The liquid residue which accumulates at the bottom of the column 19 is continuously withdrawn at the bottom and passed through a valved exit line 24 to a column 25 where the remaining low-boiling tar bases, viz, the beta and gamma picolines, lutidines and collidines distill from the mixture leaving higher boiling residues including the formaldehyde reaction products at the bottom of the column from where they were drawn off through a valved exit line 26. The vapors pass from the column through a line 27 to a condenser 28 from which colorless beta and gamma picolines, lutidines and collidines are removed by means of, a valved exit line 29. A portion of this condensate is returned to the column 25 through a valved line 30 as reflux material, the remaining condensate being withdrawn as a product mixture of these tar bases. This product mixture may have a very light yellow coloring which is due to the presence of the collidines. However, if the coloring is too severe, it is due to the presence of impurities and not to the natural color of collidines and therefore the amount of formaldehyde being added to the reactor can be increased to the point where the severe coloring is eliminated.

It is to be understood that the incoming feed stream of low-boiling tar bases and the formaldehyde can be continuously fed directly into the column 7 through valved inlet lines 31 and 32 respectively and reacted therein, if desired, instead of being reacted in a separate reaction chamber. The remainder of the process is identical with the foregoing continuous process, benzene, etc. being added to column 7 to form an azeotropic mixture of benzene and water or other solvent which is taken off the top of column 7 through line 10, the liquid residue'being withdrawn from the bottom of column 7 through valved exit line 12 and fed to column 13, etc.

Referring now to the batch process shown by the flow sheet of Fig. 2, the mixture of low-boiling tar bases is fed into a column 40 through a valved inlet line 41 and a solution of formaldehyde in water is added to the column 40 through a valved inlet line 41a from a dissolver 42. Water or other solvent, if required, is fed into the dissolver through a valved inlet line' 43. Benzene is then added to the column 40 through valved inlet line 44 from storage tank 45 in an amount sufiicient to form an azeotropic mixture with the water or other solvent, and the water already present in the low-boiling tar bases. The azeotropic mixture of benzene and solvent is then distilled from column 40 and the vapor passes through exit line 46 to condenser 47 where it is liquified and withdrawn through valved exit line 48, valved line 49 having first been closed by proper adjustment of the Valve. After the benzene-solvent constant boiling mixture has been removed, valved line 49 is opened and pyridine, alpha-picoline, and beta and gamma picolines, lutidines and collidines are successively distilled from column 40, the vapors passing from the top of the column through exit line 46 to condenser 47 where they are liquified and withdrawn through valved exit line 48. A portion of these materials is returned to the column through valved line 49 as reflux material. The high-boiling liquid residue is then withdrawn from the bottom of the column through valved line 50. Heat to effectuate the distillation is provided by heater 51.

The following specific examples are provided as being illustrative of the practice of this invention but are not to be construed as limitations thereon. Parts and percentages unless otherwise specified are given in parts and percentages by weight.

Example I A 2212 parts by weight mixture of tar bases obtained from coke plant operations containing 35% by weight of pyridine, 12.3% of piccoline, 2.7% of mixed pyrrols, 17% of beta and gamma pyridines and lutidines, and 33% of collidines and aniline is fed to a still. Three percent by weight (based on the weight of the tar base mixture) of a 40% aqueous solution of formaldehyde giving a ratio of 1.2% of aldehyde to tar bases is then added to the still. Three hundred and fifty parts of benzene is also fed to the still. Distillation is carried out at normal atmospheric pressure utilizing a 24-plate distillation column at a head temperature suflicient to distill the benzene water azeotropic mixture. Fractional distillation is then carried out at a head temperature sufficient to successively distill oif pyridine, alpha-picoline, beta and gamma picolines, lutidines, and collidines and aniline with a reflux ratio of 10:1. The fractions obtained are colorless.

Example 11 The procedure of Example I is repeated utilizing 530 parts of tar bases of the composition used in Example I, 5% by weight of paraldehyde (based on the weight of the charge of tar bases), and 132 parts by weight of benzene. The column employed has 30 theoretical plates and the reflux ratio is 10:1. The fractions of tar bases obtained are colorless.

Example 111 Example IV The procedure of Example I is repeated utilizing 505 parts of tar bases of the composition used in Example I, 1.3% by weight of acetaldehyde (based on the weight of the charge of tar bases), and 178 parts of benzene. The column employed has 24 theoretical plates and the reflux ratio is 8:1. The tar base fractions obtained are colorless.

Example V The procedure of Example I is repeated utilizing 596 parts of coke plant tar bases of the composition used in Example I, 1.5% by weight of paraformaldehyde (based on the weight of the charge of tar bases), and 173 parts of benzene. The column employed had 30 theoretical plates and the refiux ratio is :1. The tar base fractions obtained are colorless.

Data and properties of distillates of coke Plant lowboiling tar bases of the composition set forth in the foregoing examples are presented in the following table for tar base mixtures which have not been treated prior to distillation, and for tar base mixtures which have been treated before distillation with varying percentages of formaldehyde. The percentage of formaldehyde utilized is by weight and is based on the weight of the tar base charge.

Percent 0.4% Formal- 0.8% Form- 1.27 Form- Dlstllled N0 Treatment dehyde aldehyde ald hyde 2 Colorless Colorless Colorless. Colorless R do o Do. 7 do. Do. 9 do "Do. 12 Do. do Do. do Do. 28 Pale yellow--- Do. 30 do d Do. 32 do Do. 38 Light brown- (1 Do.

ish yellow. 40 Light tan do ..do Do. Tan Light brown- ...(10 Do.

lsh yellow. Deep brown- Pale yellow-.. do Do.

ish yellow. '12 Amber do do Do. i4 dn dn rln Do, Deep brown- .....(10 do Do.

ish yellow. 62 do Deep browndo Do.

ish yellow. 68 Colorless Colorless do Do. 70 do do dn D0, do do do Do. 78 !h (in (in D0, 82 dn rln do Do, 86 do do.. do Do.

If methanol or ethanol is utilized as the solvent for the formaldehyde, acetaldehyde, paraldehyde, paraformaldehyde, or mixtures thereof, the process is substantially identical as is hereinbefore described in the batch and continuous process except that a methanol or ethanol azeotrope is distilled ofi first and then the benzene-water azeotropic mixture etc.

It is to be understood that this invention is applicable to low-boiling tar base mixtures regardless of the source, for example, tar bases derived from coke-oven tar, watergas tar, and to low-boiling petroleum and shale oil tar bases, etc.

The invention claimed is:

1. A process of decolorizing and purifying mononu clear low-boiling tar bases having a pyridine nucleus which boil at a temperature of at least about C. and

' distilling the mixture to separate the aforesaid low-boiling tar bases from thhe higher-boiling reaction products of impurities.

2. The process according to claim 1 wherein the aforesaid low-boiling tar bases are treated with an approximately stoichiometric amount of formaldehyde.

3. The process according to claim 1 wherein the afore-' said low-boiling tar bases are treated with an approximately stoichiometric amount of acetaldehyde.

4. A process in accordance with claim 1 wherein the aforesaid low-boiling tar bases are treated with an approximately stoichiometric amount of propionaldehyde.

5. The processaccording to claim 1 wherein the aforesaid low-boiling tar bases are treated with an approximate- 1y stoichiometric amount of benzaldehyde.

6. The process according to claim 1 wherein the aforesaid low-boiling tar bases are treated with an approximately stoichiometric amount of toluic aldehyde.

7. The process of decolorizing and purifying mononuclear low-boiling tar bases having a pyridine nucleus which boil at a temperature of at least about 115 C. and which contain color-forming impurities comprising: treating said low-boiling tar bases with an approximately stoichiometric amount of an aldehyde containing not more than 12 carbon atoms to form higher-boiling reaction products with the color-forming impurities, incorporating an amount of benzene in the mixture that is at least sufficient to form a constant boiling mixture of benzene with the water present therein, and thereafter fractionally distilling the mixture to distill the constant boiling mixture and the aforesaid low-boiling tar bases from the mixture and leave the higher boiling reaction products of aldehyde with the color-forming impurities in the residue.

8. The process as described in claim 7 wherein the aforesaid low-boiling tar bases are treated with an approximately stoichiometric amount of formaldehyde.

9. The process according to claim 7 wherein the aforesaid low-boiling tar bases are treated with an approxi mately stoichiometric amount of acetaldehyde.

10. The process according to claim 7 wherein the aforesaid low-boiling tar bases are treated with an approximity stoichiometric amount of propionaldehyde.

11. The process as described in claim 7 wherein-the aforesaid low-boiling bases are treated with an approximately stoichiometric amount of benzaldehyde.

12. The process as described in claim 7 wherein the aforesaid low-boiling tar bases are treated with an approximately stoichiometric amount of toluic aldhyde.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Coal, Coke and Coal Chemicals, by Wilson and Wells, 1st ed. 1950, McGraw-Hill, pgs. 332 and 333. 

7. THE PROCESS OF DECOLORIZING AND PURIFYING MONONUCLEAR LOW-BOILING TAR BASES HAVING A PYRIDINE NUCLEUS WHICH BOIL AT A TEMPERATURE OF AT LEAST ABOUT 115* C. AND WHICH CONTAIN COLOR-FORMING IMPURITIES COMPRISING: TREATING SAID LOW-BOILING TAR BASES WITH AN APPROXIMATELY STOICHIOMETRIC AMOUNT OF AN ALDEHYDE CONTAINING NOT MORE THAN 12 CARBON ATOMS TO FORM HIGHER-BOILING REACTION PRODUCTS WITH THE COLOR-FORMING IMPURITIES, INCORPORATING AN AMOUNT OF BENZENE IN THE MIXTURE THAT IS AT LEAST SUFFICIENT TO FORM A CONSTANT BOILING MIXTURE OF BENZENE WITH THE WATER PRESENT THEREIN, AND THEREAFTER FRACTIONALLY DISTILLING THE MIXTURE TO DISTILL THE CONSTANT BOILING MIXTURE AND THE AFORESAID LOW-BOILING TAR BASES FROM THE MIXTURE AND LEAVE THE HIGHER BOILING REACTION PRODUCTS OF ALDEHYDE WITH THE COLOR-FORMING IMPURITIES IN THE RESIDUE. 